With the master plan and the main principles of gameplay being discussed, I want to suggest one main principle that seems to me like it was very important for Morrowind and later TES sequels too: Freedom.

In Morrowind you can drop your stuff everywhere and pick it up anytime later. You can go anywhere you want and enter any house. You can jump, fly or even teleport yourself out of trouble whenever you want. you can fully customize your own character from the beginning. You can customize your own spells and enchantments. While many of these gameplay elements have become commonplace in rpgs, some of them are still unique or rarely encountered at least.

I'm not good at describing my thoughts in an appealling way, so I will just make a small, quick listing of what I think the implications of the principle of player freedom could be for TR (assuming that you wanted to treat this as a main principle of your work) Much of what I write here, may not be entirely new and I think that a good questwriter will have some of these principles in the back of his/her mind. But anyway:

1. Design quests and general storylines with a certain flexibility in order to account for the incalculable player. Keep in mind that almost each situation can be circumvented by the player in some way or that involved npc characters can get killed or pacified anytime.

2. Design quests and general storylines in a way that players usually have several meaningful choices with an impact on the outcome.

3. Design quests and dungeons with the various possible player character types in mind. Create opportunities for the exercising of each character skill and in extension the respective spells of the magic schools. This will ideally mean that a player will have opportunities of useful application for each skill in roughly similar amounts, which in turn means that there is freedom to use and train each skill or buying special spells like sound or light without feeling stupid for doing so. Here I have several examples in mind:

Example1: An important quest item in a dungeon that can be retrieved by Telekinesis much quicker and without having to deal with a number of nasty enemies on the further way.
Example2: A quest in which you can get a favourable result of the problem by pacifying an involved hostile npc with illusion spells. Such a possibility should be specifically hinted at in dialogue, though in order to avoid dead content.
Example3: Add an obstacle that you can only pass with a certain amount of magical resistance to be achieved with the respective resistance spells. A lava sea with low ceiling (so you cannot circumvent this with levitation again) would be typical example.
Example4: Making use of darkness in dungeons to make light or infravision more useful.

4. Design shops aswell as teaching offers and high end rewards in a way that each character type gets a similar amount of interesting things. Not each smith needs to support each single armor and weapon type, but you could aim for a roughly equal distribution of armor- and weapon-types over the blacksmiths of several towns, to name an example.

5. Don't assume that the playercharacter is automatically good and wants the common good and save the world and all that stuff. Don't force the player into being the nice saviour of all, if he doesn't want to.

6. There are quite a number of interesting character profiles in the class list (pilgrim, witchhunter, monk, etc. etc.). It might be an interesting idea to mentally take the perspective of all these different character types and see what our content can offer to them, not just in terms of skill usage but also with regards to choice of acting in a situation, specifically for player that like to do roleplaying.

Agreed 100%. I think this is something we're already quite good at with quests having different possibilities for solutions, but different class types is something we should have more in mind, as well as the possibility of NPC's dying.

Well said. I think the aspect of choices wasn't something I had a major focus on when writing the main quest I have for Lyithdonea. I've been considering making some changes to it to allow flexibility for different types of player characters. So thank you for the prompt. Good thing is that I am at a stage where changes of that nature can be made painlessly.

This is good advice. Morrowind has a sliding scale - not really of good and evil, but perhaps of idealism and cynicism, or cultural attitudes - which mostly manifests in the option to take a quest or not, but should also be prevalent in the way in which quests can be completed. We should always be mindful of the limitless options players have in their game, and design situations in such a way that their chosen skills and stats are meaningful when deciding the result.